Optical transmission line monitoring device, optical transmission line monitoring method, and optical transmission line monitoring system

Abstract

To provide a method for specifying a generation position of a polarization fluctuation on an optical transmission line with high accuracy.SOLUTION: An optical transmission line monitoring device comprises: a storage part; a threshold determination part; a reference data generation part; a similar section detection part; and a position specification part. The storage part stores a first polarization state data expressing a state of a polarization detected in a local station and a second polarization state data expressing a state of the polarization of the optical transmission line detected in an opposite station. The threshold determination part detects a first time expressing a time when a polarization modulation value detected by the local station exceeds a predetermined threshold value level. The reference data generation part generates reference data by extracting neighbor data of the first time from the first polarization state data. The similar section detection part searches a section that is similar to the reference data in the second polarization state data, and this detects a second time expressing a time when a polarization modulation component arrives at the opposite station. The position specification part specifies a polarization modulation position on the basis of the first and second times.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to an apparatus and method for monitoring an optical transmission line. [Background technology]

[0002] In optical communication systems, coherent transmission has become mainstream due to the increasing transmission speed. In coherent transmission, signals are transmitted using the phase and polarization of light. Therefore, if the polarization changes suddenly on the optical transmission line, burst errors may occur at the receiving node.

[0003] Furthermore, as the transmission capacity of networks increases, modulation methods that allow each symbol to transmit a large number of bits are being adopted. However, in optical communications using such modulation methods, polarization fluctuations caused by the vibration of optical fibers or lightning strikes can have a significant impact on communication quality. For this reason, technology that identifies the position where polarization fluctuations occur on an optical transmission path has attracted attention (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-043154 A Summary of the Invention [Problem to be solved by the invention]

[0005] The position where the polarization fluctuation occurs (polarization fluctuation position) is identified, for example, based on the timing at which the polarization fluctuation is detected in a pair of terminal nodes connected to both ends of the optical transmission line. However, the states of polarization (SOP: State of Polarization) detected in a pair of terminal nodes are not the same. For this reason, there may be cases where the polarization fluctuation is detected in one terminal node but not in the other terminal node. In this case, it is not possible to identify the polarization fluctuation position, or at least it is difficult to identify the polarization fluctuation position with high accuracy.

[0006] This problem can be solved, for example, by increasing the receiving sensitivity of each end node. However, in this case, there is a risk that noise on the optical transmission line may be determined to be a polarization fluctuation. Alternatively, multiple polarization fluctuation triggers may be detected for one polarization fluctuation event, and the identified polarization fluctuation position may have a large error.

[0007] An object of one aspect of the present invention is to provide a method for accurately identifying a polarization fluctuation position on an optical transmission line. [Means for solving the problem]

[0008] An optical transmission line monitoring device according to one aspect of the present invention is mounted in a first end node of a pair of end nodes in an optical transmission system for transmitting frames bidirectionally via an optical transmission line between the pair of end nodes. This optical transmission line monitoring device includes a polarization state monitor that monitors the polarization state of the optical transmission line, a first storage unit that stores first polarization state data representing the polarization state detected by the polarization state monitor, a second storage unit that stores second polarization state data representing the polarization state of the optical transmission line detected by an opposite station device mounted in a second end node of the pair of end nodes, and a polarization fluctuation value that represents the fluctuation speed of the polarization detected by the polarization state monitor and a predetermined threshold level, thereby detecting when a polarization fluctuation component caused by a polarization fluctuation occurring in the optical transmission line has arrived at the optical transmission line monitoring device. the first polarization state data generating unit generating reference data by extracting the first polarization state data near the first time from the first polarization state data; a similar section detecting unit detecting a second time representing the time at which a polarization fluctuation component caused by the polarization fluctuation arrived at the opposite station device by searching for a section in the second polarization state data having a polarization state similar to the polarization state represented by the reference data; and a position identifying unit identifying a polarization fluctuation position representing the position at which the polarization fluctuation occurred based on the first time and the second time. Effect of the Invention

[0009] According to the above aspect, the position of polarization fluctuation on the optical transmission line can be identified with high accuracy. [Brief description of the drawings]

[0010] [Figure 1] FIG. 11 is a diagram illustrating an example of a method for identifying the location where polarization fluctuation occurs. [Diagram 2] FIG. 13 is a diagram illustrating an example of a configuration for identifying a polarization fluctuation position. [Diagram 3] FIG. 1 illustrates an example of a method for monitoring polarization fluctuations. [Figure 4] FIG. 1 illustrates an example of frame transmission between optical transmission devices (part 1). [Diagram 5] FIG. 2 illustrates an example of frame transmission between optical transmission devices (part 2). [Figure 6] FIG. 3 is a diagram (part 3) illustrating an example of frame transmission between optical transmission devices. [Figure 7] FIG. 13 is a diagram illustrating an example of a method for identifying a polarization fluctuation position. [Figure 8] 1 is a diagram illustrating a problem with a method for detecting polarization fluctuation at both end nodes. [Figure 9] 1 is a diagram for explaining an outline of an optical transmission line monitoring method according to an embodiment of the present invention; [Figure 10] FIG. 2 is a diagram illustrating an example of a functional configuration of an opposite station device. [Figure 11] FIG. 11 is a diagram illustrating an example of polarization state data. [Figure 12] FIG. 2 illustrates an example of a functional configuration of an optical transmission line monitoring device. [Figure 13] 11 is a diagram showing an example of opposite station polarization state data stored in an opposite station data storage unit; FIG. [Figure 14] FIG. 13 is a diagram illustrating an example of a method for generating reference data. [Figure 15] FIG. 13 is a diagram illustrating an overview of the process of a similar section detection unit. [Figure 16] 11 is a diagram illustrating a search period by a similar section detection unit. FIG. [Figure 17] 11A and 11B are diagrams illustrating an example of processing by a similar section detection unit; [Figure 18] 13 is a flowchart illustrating an example of processing by a similar section detection unit. [Figure 19] 13 is a flowchart showing an example of a process for comparing a reference SOP waveform with an opposing station SOP waveform. [Figure 20] FIG. 13 is a diagram illustrating an example of a method for identifying a polarization fluctuation position. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 1 shows an example of a method for identifying the location where polarization fluctuation occurs. In this example, an optical transmission system includes an optical transmission device (NE) 1A and an optical transmission device (NE) 1B. The optical transmission device 1A and the optical transmission device 1B are connected to each other by an optical transmission path 2. That is, the optical transmission device 1A and the optical transmission device 1B are provided at both ends of the optical transmission path 2.

[0012] The optical transmission path 2 is composed of a pair of optical fibers 2x and 2y. The optical fiber 2x propagates an optical signal from the optical transmission device 1A to the optical transmission device 1B, and the optical fiber 2y propagates an optical signal from the optical transmission device 1B to the optical transmission device 1A. The optical fiber 2x and the optical fiber 2y are laid adjacent to each other. Although not particularly limited, the optical fiber 2x and the optical fiber 2y are housed in the same cable.

[0013] Here, as shown in Fig. 1(a), it is assumed that at time T0, the state of polarization (SOP) of the optical transmission line 2 changes suddenly. In Fig. 1, P0 represents the position where the polarization change occurs. In the following description, the position where the polarization change occurs may be referred to as the "polarization change position."

[0014] Fluctuations in polarization in the optical transmission line 2 affect the polarization state of the light propagating through the optical fibers 2x and 2y. In the following description, the optical component whose polarization state has been affected in the optical fiber 2x may be referred to as a polarization fluctuation component 3x, and the optical component whose polarization state has been affected in the optical fiber 2y may be referred to as a polarization fluctuation component 3y.

[0015] The polarization fluctuation component 3x propagates from position P0 toward the optical transmission device 1B through the optical fiber 2x. The polarization fluctuation component 3y propagates from position P0 toward the optical transmission device 1A through the optical fiber 2y. Therefore, as shown in FIG. 1(b), the polarization fluctuation components 3x and 3y each reach a position a predetermined distance away from position P0 at time T1.

[0016] Thereafter, the polarization fluctuation component 3x arrives at the optical transmission device 1B at time T2, as shown in FIG. 1(c). Moreover, the polarization fluctuation component 3y arrives at the optical transmission device 1A at time T3, as shown in FIG. 1(d). Then, the position P0 can be calculated based on the difference ΔT (=T3-T2) between the time T2 and the time T3. Here, it is assumed that the propagation time TL of the light between the optical transmission devices 1A and 1B is obtained by measurement or calculation. In this case, the propagation time "T(A-P0)" between the optical transmission device 1A and the position P0 is expressed by the following formula (1).

number

[0017] Furthermore, the distance "D(A-P0)" between the optical transmission device 1A and the position P0 is expressed by the following formula (2): n represents the refractive index of the optical fiber, and c represents the speed of light in a vacuum.

number

[0018] In this way, by measuring the time when the polarization fluctuation is detected at the nodes on both ends of the optical transmission line 2, the polarization fluctuation position P0 can be identified.

[0019] 2 shows an example of a configuration for identifying a polarization fluctuation position. Here, optical transmission devices (1A, 1B) are implemented at the end nodes of an optical transmission line 2. In the following description, each optical transmission device may be referred to as "NE (Network Element)."

[0020] 1, the optical transmission path 2 includes an optical fiber 2x that propagates an optical signal from the optical transmission device 1A to the optical transmission device 1B, and an optical fiber 2y that propagates an optical signal from the optical transmission device 1B to the optical transmission device 1A. The optical fibers 2x and 2y have the same length and are laid on the same route. The optical fibers 2x and 2y are housed in the same cable. For example, an OTN (Optical Transport Network) frame is transmitted between the optical transmission devices 1A and 1B.

[0021] The optical transmission device 1A includes a counter 11A, a frame generating unit 12A, a transmitting unit 13A, a receiving unit 14A, and a polarization state monitor 15A. The optical transmission device 1A may include other functions, circuits, or devices not shown in Fig. 2. For example, the optical transmission device 1A includes a frame pulse generating circuit that generates a frame pulse at a predetermined period.

[0022] The counter 11A is a free-running counter that operates in response to the above-mentioned frame pulse. As an example, the counter 11A outputs a counter value that is incremented in response to the frame pulse.

[0023] The frame generator 12A generates overhead for a transmission frame in response to the frame pulse, and inserts the counter value output from the counter 11A into this overhead.

[0024] The transmitter 13A transmits a frame including a payload in which the overhead and data generated by the frame generator 12A are stored to the optical transmission device 1B. That is, the counter value notified by the optical transmission device 1A is notified to the optical transmission device 1B.

[0025] The receiving unit 14A receives a frame transmitted from the optical transmission device 1B. The receiving unit 14A then extracts a counter value from the overhead of the received frame. The optical transmission device 1A and the optical transmission device 1B have substantially the same configuration. That is, a counter value generated by the counter 11B of the optical transmission device 1B is inserted into the overhead of a frame transmitted from the optical transmission device 1B to the optical transmission device 1A. Therefore, the receiving unit 14A can extract the counter value generated by the counter 11B of the optical transmission device 1B from the received frame.

[0026] The polarization state monitor 15A monitors the state of polarization occurring in the optical transmission path between the optical transmission device 1A and the optical transmission device 1B by using the optical signal received from the optical transmission device 1B. Note that the polarization state monitor 15A may be implemented, for example, in a receiver that recovers symbols from the received optical signal.

[0027] 3 shows an example of a method for monitoring polarization fluctuation. The polarization fluctuation is detected in a receiver that receives an optical signal via an optical transmission line 2. In this embodiment, the receiver includes a 90-degree optical hybrid circuit 21, a fixed equalizer 22, an adaptive equalizer 23, a phase estimation unit 24, a determination unit 25, and a fluctuation determination unit 26.

[0028] The 90-degree optical hybrid circuit 21 generates an electrical signal representing the electric field of the received optical signal by using a local light source (not shown). The fixed equalizer 22 equalizes the output signal of the 90-degree optical hybrid circuit 21. For example, the fixed equalizer 22 compensates for chromatic dispersion and the like. The adaptive equalizer 23 includes a digital filter such as an FIR filter, and adaptively equalizes the output signal of the fixed equalizer 22. The adaptive equalizer 23 also performs polarization separation. At this time, the coefficient of each tap of the digital filter is updated based on the input signal and output signal of the adaptive equalizer 23.

[0029] The phase estimator 24 compensates for the phase offset of the output signal of the adaptive equalizer 23. This recovers the phase of each symbol. The determiner 25 recovers the data assigned to each symbol in the transmitting node based on the output signal of the phase estimator 24.

[0030] The fluctuation determining unit 26 monitors the polarization fluctuation occurring in the optical transmission path 2 between the optical transmission device 1A and the optical transmission device 1B based on the output signal of the adaptive equalizer 23 or the tap coefficient of the digital filter constituting the adaptive equalizer 23. Then, the fluctuation determining unit 26 outputs a polarization fluctuation detection flag when the polarization fluctuation level (or the polarization fluctuation speed) is greater than a predetermined threshold level. In other words, the polarization fluctuation detection flag indicates that a polarization fluctuation greater than a predetermined threshold level has occurred in the optical transmission path between the optical transmission device 1A and the optical transmission device 1B.

[0031] The fluctuation determining unit 26 (or the polarization state monitor) is realized, for example, by a hardware circuit that processes digital signals. Alternatively, the fluctuation determining unit 26 is realized by a processor system including a processor and a memory. In this case, the processor provides the function of the fluctuation determining unit 26 by executing a program that outputs a polarization fluctuation detection flag when a polarization fluctuation is detected.

[0032] 3. Alternatively, the polarization state monitor 15A corresponds to the 90-degree optical hybrid circuit 21, the fixed equalizer 22, the adaptive equalizer 23, and the fluctuation determining unit 26. The polarization state monitor 15A outputs a polarization fluctuation detection flag when a polarization fluctuation greater than a predetermined threshold level occurs in the optical transmission path between the optical transmission device 1A and the optical transmission device 1B.

[0033] The polarization fluctuation detection flag is set in the overhead of a transmission frame by the frame generating unit 12A. Then, the frame in which the counter value and the polarization fluctuation detection flag are set is transmitted to the optical transmission device 1B. Thus, the optical transmission device 1B can obtain the counter value of the optical transmission device 1A when the optical transmission device 1A detects polarization fluctuation.

[0034] The optical transmission device 1B includes a counter 11B, a frame generator 12B, a transmitter 13B, a receiver 14B, and a polarization state monitor 15B. That is, the configuration of the optical transmission device 1B is substantially the same as that of the optical transmission device 1A. The counter 11A implemented in the optical transmission device 1A and the counter 11B implemented in the optical transmission device 1B perform counting operations independently of each other. However, the counters 11A and 11B perform counting operations at the same cycle.

[0035] The operation of the optical transmission device 1B is substantially the same as that of the optical transmission device 1A. Therefore, the optical transmission device 1B also monitors the polarization fluctuation occurring in the optical transmission line 2. When the optical transmission device 1B detects a polarization fluctuation greater than a threshold level, the optical transmission device 1B transmits a counter value and a frame in which a polarization fluctuation detection flag is set to the optical transmission device 1A. Therefore, the optical transmission device 1A can obtain the counter value of the optical transmission device 1B at the time when the optical transmission device 1B detected the polarization fluctuation.

[0036] 4 to 6 show an example of frame transmission between optical transmission devices 1A and 1B. Here, counters 11A and 11B each perform a counting operation at a predetermined period ΔT. In this embodiment, period ΔT is 10 μsec. That is, counters 11A and 11B perform a counting operation at 10 μsec intervals.

[0037] At time T0, it is assumed that the counter value AFC output from the counter 11A implemented in the optical transmission device 1A is “110.” Then, the optical transmission device 1A transmits a frame including this counter value to the optical transmission device 1B.

[0038] A frame transmitted from the optical transmission device 1A propagates a distance ΔD in the optical fiber during a period ΔT. That is, at time T1 (T0+ΔT), the frame arrives at a position (P1 in FIG. 4) that is ΔD away from the optical transmission device 1A. Here, in this example, ΔT is 10 μsec. Also, assume that the speed of light is 300,000 km / sec and the refractive index of the optical fiber is 1.43. In this case, ΔD is approximately 2 km.

[0039] In this way, the transmission frame propagates a distance ΔD during the period ΔT. That is, the transmission frame passes position P2 (a position 2ΔD away from the optical transmission device 1A) at time T2 (T0+2ΔT), and passes position P3 (a position 3ΔD away from the optical transmission device 1A) at time T3 (T0+3ΔT). Then, in this embodiment, the transmission frame arrives at the optical transmission device 1B at time T10 (T0+10ΔT). Here, ΔD is 2 km. Therefore, the transmission distance between the optical transmission devices 1A and 1B is 20 km.

[0040] The counter 11A performs a counting operation with a period ΔT. That is, the counter value AFC output from the counter 11A is incremented with a period ΔT. For example, as shown in FIG. 5, in a case where the counter value AFC generated at time T0 is "110", the counter value AFC generated at time T1 (T0+ΔT) is "111", and the counter value AFC generated at time T2 (T0+2ΔT) is "112". Then, every time a new counter value is generated, the optical transmission device 1A generates a frame including each counter value and transmits it to the optical transmission device 1B. In the following description, a frame with a counter value of "i" inserted in the overhead may be referred to as "frame i".

[0041] As described above, each frame transmitted from the optical transmission device 1A propagates a distance ΔD in the optical fiber during the period ΔT. Therefore, for example, a frame 110 transmitted from the optical transmission device 1A at time T0 arrives at a position P1 at time T1 and arrives at a position P2 at time T2. Also, a frame 111 transmitted from the optical transmission device 1A at time T1 arrives at a position P1 at time T2 and arrives at a position P2 at time T3.

[0042] Therefore, at time Ti (i=0, 1, 2...), frames are located at positions P0 to P10. For example, at time T1, frames 111 to 101 are located at positions P0 to P10, respectively. Furthermore, at time T2, frames 112 to 102 are located at positions P0 to P10, respectively. Note that positions P0 and P10 represent the positions of optical transmission device 1A and optical transmission device 1B, respectively.

[0043] Like the optical transmission device 1A, the optical transmission device 1B generates a frame including a counter value BFC generated by the counter 11B and transmits the frame to the optical transmission device 1A. However, the counter 11A implemented in the optical transmission device 1A and the counter 11B implemented in the optical transmission device 1B perform counting operations independently of each other. Therefore, the counter values ​​generated by the counters 11A and 11B at a certain time are usually different from each other.

[0044] 6, at time T0, the counter value AFC generated by the counter 11A in the optical transmission device 1A is "110," and the counter value BFC generated by the counter 11B in the optical transmission device 1B is "210." Furthermore, at time T1, the counter value AFC generated by the counter 11A in the optical transmission device 1A is "111," and the counter value BFC generated by the counter 11B in the optical transmission device 1B is "211."

[0045] A frame transmitted from the optical transmission device 1B propagates from the optical transmission device 1B toward the optical transmission device 1A a distance ΔD in the optical fiber during a period ΔT. Thus, for example, a frame 210 transmitted from the optical transmission device 1B at time T0 reaches a position P9 at time T1, and a position P8 at time T2. A frame 211 transmitted from the optical transmission device 1B at time T1 reaches a position P9 at time T2, and a position P8 at time T3. Thus, for example, at time T1, frames 211 to 201 are located at positions P10 to P0, respectively. At time T2, frames 212 to 202 are located at positions P10 to P0, respectively.

[0046] In the optical network in which the above-mentioned frame transmission is performed, the optical transmission devices 1A and 1B each monitor the state of polarization. When a polarization fluctuation occurs in the optical transmission line 2, the optical transmission devices 1A and 1B each detect the polarization fluctuation.

[0047] FIG. 7 shows an example of a method for identifying a polarization fluctuation position. In this example, an optical transmission path 2 is provided between optical transmission devices 1A and 1B. The length of the optical transmission path 2 (i.e., the distance D between the optical transmission devices 1A and 1B) is 10ΔD. ΔD is the distance that light propagates through the optical transmission path 2 during a period ΔT corresponding to a frame transmission period. In FIG. 7, AFC represents a counter value output by the counter 11A in the optical transmission device 1A. BFC represents a counter value output by the counter 11B in the optical transmission device 1B. Received BFC represents a counter value BFC received by the optical transmission device 1A from the optical transmission device 1B. In this embodiment, it is assumed that the optical transmission device 1A identifies the polarization fluctuation position.

[0048] At time T0, polarization fluctuation occurs at position P6. Position P6 is a position 6ΔD away from the optical transmission device 1A and a position 4ΔD away from the optical transmission device 1B. Note that at time T0, the counter value AFC of the optical transmission device 1A is "15," and the counter value BFC of the optical transmission device 1B is "31." Thereafter, the polarization fluctuation component 3x propagates toward the optical transmission device 1B via the optical transmission path 2, and the polarization fluctuation component 3y propagates toward the optical transmission device 1A via the optical transmission path 2.

[0049] Each of the optical transmission devices 1A and 1B transmits its own counter value to the opposite device via the optical transmission path 2. In this embodiment, the time it takes for a frame to propagate from the optical transmission device 1B to the optical transmission device 1A is 10ΔT. Therefore, the counter value BFC that the optical transmission device 1A receives from the optical transmission device 1B at time T0 is "21."

[0050] At time T1 (time T0+ΔT), the polarization fluctuation component 3x arrives at a position ΔD away from position P6 toward the optical transmission device 1B, and the polarization fluctuation component 3y arrives at a position ΔD away from position P6 toward the optical transmission device 1A. At this time, the counter value AFC of the optical transmission device 1A is "16," and the counter value BFC of the optical transmission device 1B is "32."

[0051] At time T2 (T0+4ΔT), the polarization fluctuation component 3x arrives at the optical transmission device 1B. Therefore, the optical transmission device 1B detects polarization fluctuation greater than the threshold level at time T2. At this time, the counter value BFC of the optical transmission device 1B is "35." Therefore, at time T2, the optical transmission device 1B generates a frame into which "BFC=35" and a polarization fluctuation detection flag are inserted, and transmits the frame to the optical transmission device 1A.

[0052] At time T3 (T0+6ΔT), the polarization fluctuation component 3y arrives at the optical transmission device 1A. Therefore, the optical transmission device 1A detects a polarization fluctuation greater than the threshold level at time T6. Thereafter, the optical transmission device 1A waits for a polarization fluctuation detection flag to be transmitted from the optical transmission device 1B.

[0053] The propagation time between the optical transmission devices 1A and 1B is 10ΔT. Therefore, the frame with "BFC=35" and the polarization fluctuation detection flag inserted, transmitted from the optical transmission device 1B at time T2, arrives at the optical transmission device 1A at time T4 (T2+10ΔT). As a result, the optical transmission device 1A recognizes that the optical transmission device 1B detected polarization fluctuation when the counter value BFC of the optical transmission device 1B was "35." On the other hand, the optical transmission device 1A detects polarization fluctuation at time T3.

[0054] The optical transmission device 1A calculates the difference between the counter value BFC (reception counter value BFC) set in the frame received from the optical transmission device 1B at the time when the polarization fluctuation was detected (i.e., T3) and the counter value BFC (reception counter value BFC) of the optical transmission device 1B when the optical transmission device 1B detected the polarization fluctuation. In this embodiment, the reception counter value BFC acquired at the time T3 when the optical transmission device 1A detected the polarization fluctuation is "27". Also, the counter value BFC when the optical transmission device 1B detected the polarization fluctuation is "35". Therefore, the difference is "8". Furthermore, by dividing this difference by "2", the propagation time between the polarization fluctuation position and the optical transmission device 1B is obtained. In this embodiment, "4" is obtained. Therefore, it is determined that the polarization fluctuation position is away from the optical transmission device 1B by 4ΔD. In this way, according to the configuration shown in FIG. 2, the polarization fluctuation position is identified by detecting the polarization fluctuation at both end nodes of the optical transmission line 2.

[0055] However, when polarization fluctuation occurs in the optical transmission line 2, the polarization fluctuation speed (or polarization fluctuation level) detected at one end node may differ from the polarization fluctuation speed detected at the other end node. For example, in the case shown in FIG. 8, the polarization fluctuation level detected at the optical transmission device 1B is smaller than the polarization fluctuation level detected at the optical transmission device 1A. Here, the optical transmission devices 1A and 1B determine that polarization fluctuation has occurred in the optical transmission line 2 when the detected polarization fluctuation level is greater than a predetermined threshold level. In this example, as shown in FIG. 8, the polarization fluctuation level detected at the optical transmission device 1A is greater than the threshold level, but the polarization fluctuation level detected at the optical transmission device 1B is smaller than the threshold level.

[0056] In this case, the optical transmission device 1A detects the polarization fluctuation, but the optical transmission device 1B does not detect the polarization fluctuation. As a result, the optical transmission device 1A cannot identify the polarization fluctuation position by the method shown in Fig. 7. Therefore, the optical transmission line monitoring device according to the embodiment of the present invention has a function to solve this problem.

[0057] FIG. 9 is a diagram for explaining an outline of an optical transmission line monitoring method according to an embodiment of the present invention. In this example, an optical transmission line monitoring device is provided at one of the terminal nodes of an optical transmission line 2. The optical transmission line monitoring device may be implemented, for example, in an optical transmission device. In the following description, the other terminal node of the optical transmission line 2 may be called an "opposite station." Also, a device provided at the opposite station to identify the polarization fluctuation position may be called an "opposite station device." The opposite station device is implemented in the optical transmission device.

[0058] The optical transmission line monitoring device continuously monitors the state of polarization of the optical transmission line 2 based on the received optical signal. The monitoring results are stored in a chronological order in a FIFO (First-In First-Out) memory. At this time, a polarization fluctuation value that indicates a change in the state of polarization is sampled at a predetermined period and written to the FIFO memory. This allows polarization state data that indicates a change in the polarization state over time to be obtained. FIG. 9(a) shows the polarization state data detected by the optical transmission line monitoring device. In the following description, the polarization state data detected by the optical transmission line monitoring device may be referred to as "local SOP data". Also, the waveform represented by the local SOP data may be referred to as "local SOP waveform". The sampling timing in the optical transmission line monitoring device is represented by the counter value of a counter provided in the optical transmission line monitoring device.

[0059] The opposite station device also monitors the state of polarization of the optical transmission line 2 based on the received optical signal. Then, the opposite station device transmits the monitoring result to the optical transmission line monitoring device. That is, the polarization state data obtained in the opposite station device is transmitted from the opposite station device to the optical transmission line monitoring device. FIG. 9(b) shows the polarization state data detected by the opposite station device. In the following description, the polarization state data detected by the opposite station device may be referred to as "opposite station SOP data". Also, the waveform represented by the opposite station SOP data may be referred to as "opposite station SOP waveform". Also, the sampling timing in the opposite station device is represented by the counter value of a counter provided in the opposite station device.

[0060] As shown in FIG. 9(a), the optical transmission line monitoring device compares the polarization fluctuation level (or polarization fluctuation speed) detected in the local station with a predetermined threshold level. Then, when a polarization fluctuation level higher than the threshold level is detected, the optical transmission line monitoring device determines that polarization fluctuation has occurred in the optical transmission line 2. In this case, the optical transmission line monitoring device extracts a waveform in a period near the time when the polarization fluctuation level exceeds the threshold level from the local station SOP waveform. In this embodiment, the polarization fluctuation level exceeds the threshold level at time Tn. Then, the local station SOP waveform in the period from time Tn-N to time Tn+N is extracted. In the following description, the waveform extracted in this manner may be called a "reference SOP waveform."

[0061] It is preferable that N, which defines the period of the reference SOP waveform, is determined based on the polarization fluctuation that can actually occur in the optical transmission line 2. For example, the period during which polarization fluctuation occurs due to a lightning strike is several tens of microseconds. Therefore, N may be approximately several tens of microseconds to 100 microseconds. Note that N may be a value converted into a frame period.

[0062] Next, the optical transmission line monitoring device searches for a section in the opposing station SOP waveform that has a waveform similar to the reference SOP waveform. In this embodiment, the opposing station SOP waveform at time Tm±N shown in FIG. 9(b) is similar to the reference SOP waveform. In this case, the optical transmission line monitoring device determines that the time Tm of the opposing station SOP waveform corresponds to the time Tn of the local station SOP waveform. That is, the optical transmission line monitoring device estimates that the opposing station device detected a polarization fluctuation at time Tm.

[0063] Here, Tn shown in Fig. 9(a) represents the time when the optical transmission line monitoring device detects the polarization fluctuation, and corresponds to the counter value AFC "21" shown in Fig. 7. Moreover, Tm shown in Fig. 9(b) represents the time when the opposite station device detects the same polarization fluctuation, and corresponds to the counter value BFC "35" shown in Fig. 7. Therefore, the optical transmission line monitoring device can identify the polarization fluctuation position by the method described with reference to Fig. 7.

[0064] Fig. 10 shows an example of a method for generating opposite station SOP data in an opposite station. In this example, an opposite station device 30 provided in the opposite station includes a polarization state monitor 31, a frame synchronization unit 32, a frame counter 33, a multiplier 34, a sampling circuit 35, a FIFO circuit 36, an SOP data generation unit 37, and a transmission OH generation unit 38. The opposite station device 30 may include other circuits, devices, or functions not shown in Fig. 10. The opposite station device 30 is implemented in an optical transmission device such as a transponder. The transponder includes an optical transmitter, an optical receiver, and a processor such as a DSP (Digital Signal Processor).

[0065] The polarization state monitor 31 monitors the state of polarization in the optical transmission line based on the received optical signal. The polarization state monitor 31 monitors the state of polarization in the optical transmission line based on, for example, the output signal of the adaptive equalizer 23 shown in Fig. 3 or the tap coefficient of a digital filter constituting the adaptive equalizer 23. The polarization state monitor 31 then calculates the change in the polarization state at a predetermined time interval to output an SOP fluctuation value. The SOP fluctuation value corresponds to the polarization fluctuation speed (or the polarization fluctuation level) that indicates the speed of the polarization fluctuation.

[0066] The frame synchronization unit 32 generates a frame pulse at a predetermined frame period. The frame period indicates a transmission period of a frame transmitted through the optical transmission line 2.

[0067] The frame counter 33 outputs a counter value that is incremented in accordance with the frame pulse. In the following description, the counter value output from the frame counter 33 may be denoted as "FC."

[0068] The frequency multiplier 34 generates a 16-fold frame pulse having a frequency 16 times that of the frame pulse, based on the frame pulse.

[0069] The sampling circuit 35 includes a frame decimal counter 35a. The frame decimal counter 35a outputs a counter value that is incremented according to a 16-fold frame pulse. Here, the frame decimal counter 35a cyclically outputs values ​​from 0 to 15. In the following description, the counter value output from the frame decimal counter 35a may be referred to as "FDC."

[0070] Moreover, the sampling circuit 35 samples the SOP variation value in accordance with the 16-fold frame pulse, and outputs the sampled SOP variation value with a counter value FDC.

[0071] The FIFO circuit 36 ​​chronologically stores the SOP variation values ​​output from the polarization state monitor 31. At this time, each SOP variation value is stored in association with a counter value FC output from the frame counter 33 and a counter value FDC output from the frame decimal counter 35a. The pair of counter value FC and counter value FDC is used as time information indicating time.

[0072] The SOP data generator 37 generates the opposite station SOP data by reading the SOP variation value, the counter value FC, and the counter value FDC from the FIFO circuit 36 ​​in a frame cycle. Therefore, the opposite station SOP data generated in a frame cycle includes one set of SOP variation values ​​(16 SOP variation values ​​in this example) as shown in Fig. 11(a). In addition, each SOP variation value is given a corresponding counter value FC and counter value FDC. The counter value FC and counter value FDC essentially represent the time when the SOP variation value was detected.

[0073] In the opposing station SOP data shown in Fig. 11(a), the counter values ​​FC assigned to the 16 SOP variables are the same. Also, the counter value FDC cyclically represents values ​​from 0 to 15. Therefore, if the counter value FC and counter value FDC assigned to one value (e.g., SOP_1) of the 16 SOP variables are known, the counter values ​​FC and counter value FDC assigned to the other 15 SOP variables are each uniquely determined. Therefore, the opposing station SOP data corresponding to one transmission frame may be composed of 16 SOP variables, one counter value FC, and one counter value FDC, as shown in Fig. 11(b).

[0074] The transmission OH generating unit 38 generates overhead for the transmission frame. At this time, the transmission OH generating unit 38 inserts the opposing station SOP data generated by the SOP data generating unit 37 into a predetermined area in the overhead. Note that, if the opposing station SOP data shown in Fig. 11(b) is used, the amount of information of the data to be inserted into the overhead of the transmission frame can be reduced.

[0075] The opposite station device 30 transmits frames to the optical transmission line monitoring device via the optical transmission line 2 at the above-mentioned frame period. At this time, the opposite station SOP data shown in Fig. 11 is inserted in the overhead of each frame. Therefore, the optical transmission line monitoring device can obtain the opposite station SOP data indicating the state of polarization detected at the opposite station.

[0076] Fig. 12 shows an example of a functional configuration of an optical transmission line monitoring device according to an embodiment of the present invention. In this embodiment, the optical transmission line monitoring device 40 includes a polarization state monitor 41, a frame synchronization unit 42, a frame counter 43, a multiplier 44, a sampling circuit 45, a FIFO circuit 46, an opposite station data storage unit 47, a threshold determination unit 48, a reference data generation unit 49, a similar section detection unit 50, and a position specification unit 51. The optical transmission line monitoring device 40 may include other circuits, devices, or functions not shown in Fig. 12. The optical transmission line monitoring device 40 is implemented in an optical transmission device such as a transponder, for example.

[0077] The functions of the polarization state monitor 41, the frame synchronizer 42, the frame counter 43, the multiplier 44, the sampling circuit 45, and the FIFO circuit 46 are substantially the same as the functions of the polarization state monitor 31, the frame synchronizer 32, the frame counter 33, the multiplier 34, the sampling circuit 35, and the FIFO circuit 36 ​​shown in Fig. 10. Therefore, the FIFO circuit 46 stores the local station SOP fluctuation values ​​detected in the optical transmission line monitoring device 40 in chronological order.

[0078] The opposite station data storage unit 47 stores the opposite station SOP variation values ​​detected at the opposite station in chronological order. Here, the opposite station device 30 generates the opposite station SOP data shown in FIG. 11 for each frame period, as described with reference to FIG. 10. The opposite station device 30 also inserts the opposite station SOP data into the overhead of each frame and transmits it to the optical transmission path monitoring device 40. Then, the optical transmission path monitoring device 40 extracts the opposite station SOP data from each received frame and stores it in the opposite station data storage unit 47 in order.

[0079] In this embodiment, the opposite station data storage unit 47 is a FIFO memory. In this case, for example, the latest 16M opposite station SOP variation values ​​are stored in the opposite station data storage unit 47. M represents the number of frames present on the optical transmission line when frames are transmitted in both directions between the optical transmission line monitoring device 40 and the opposite station at a predetermined period. That is, M is obtained by dividing the RTT (Round Trip Time) between the optical transmission line monitoring device 40 and the opposite station by the frame transmission period. Here, 16 opposite station SOP variation values ​​are inserted in the overhead of each frame. Therefore, the opposite station data storage unit 47 stores the opposite station SOP variation values ​​extracted from the latest M received frames, as shown in FIG. 13.

[0080] It is preferable that the optical transmission line monitoring device 40 measures the RTT between the optical transmission line monitoring device 40 and the opposite station in advance. The method of measuring the RTT is not particularly limited, but in the case where the optical transmission system transmits an OTN (Optical Transport Network) frame, the delay measurement function of the OTN can be used.

[0081] The threshold value determination unit 48 compares the local SOP fluctuation value detected by the polarization state monitor 41 with a predetermined threshold level. Then, when the local SOP fluctuation value exceeds the threshold level, the threshold value determination unit 48 outputs a trigger signal. That is, when the optical transmission line monitoring device 40 detects a polarization fluctuation larger than the predetermined threshold level, the threshold value determination unit 48 outputs a trigger signal.

[0082] When the reference data generating unit 49 receives a trigger signal, as shown in FIG. 14, it generates reference data by reading out the local SOP variation value detected in a predetermined period near the trigger signal from the FIFO circuit 46. Here, it is preferable to determine the range in which the local SOP variation value is read out from the FIFO circuit 46 to generate the reference data so as to include a period in which the polarization varies greatly due to a specific cause in the optical transmission line 2. For example, the period in which the polarization variation occurs due to a lightning strike is several tens of microseconds. Therefore, in this case, for example, if the local SOP variation value detected in each of 100 microseconds immediately before and after the time when the trigger signal is output (i.e., the time when the optical transmission line monitoring device 40 detects the local SOP variation value larger than the threshold level) is obtained, the waveform of the polarization variation due to a lightning strike or the like (reference SOP waveform) can be obtained.

[0083] In this embodiment, the range in which the local SOP variation values ​​are read from the FIFO circuit 46 to generate the reference data is determined based on the frame transmission period. Specifically, N shown in FIG. 14 is expressed as a value converted into the period of the frame decimal counter 45a. The period of the frame decimal counter 45a is 1 / 16 of the frame transmission period. Therefore, for example, when "100 μsec" is converted into the period of the frame decimal counter 45a, N is 160. In this case, the reference data is composed of 320 local SOP variation values ​​in the vicinity of the trigger signal. That is, the reference SOP waveform is represented by 320 local SOP variation values ​​in the vicinity of the trigger signal.

[0084] The similar section detection unit 50 detects the time when the polarization fluctuation generated in the optical transmission line 2 arrives at the opposite station by searching for a section having a polarization state similar to the polarization state represented by the reference data (i.e., the reference SOP waveform) in the opposite station SOP data representing the state of polarization detected at the opposite station. Here, the opposite station SOP data is stored in the opposite station data storage unit 47.

[0085] 15 shows an overview of the processing of the similar section detection unit 50. The similar section detection unit 50 searches for a section having a waveform similar to that of the reference data in the opposite station SOP data. The similar section detection unit 50 searches for a section similar to the reference data while shifting the reference data relative to the opposite station SOP data. The search is started when a trigger signal is generated (i.e., when the optical transmission line monitoring device 40 detects a local station SOP fluctuation value greater than the threshold level). The search period is "16M" when converted into the period of the frame decimal counter 45a.

[0086] 16 is a diagram illustrating a search period by the similar section detection unit 50. In this case, polarization fluctuation occurs at time T0. Thereafter, the polarization fluctuation component 3x propagates toward the opposite station device 30, and the polarization fluctuation component 3y propagates toward the optical transmission line monitoring device 40. At time T1, the polarization fluctuation component 3y arrives at the optical transmission line monitoring device 40. At this time, the optical transmission line monitoring device 40 detects that polarization fluctuation has occurred. Then, at time T2, the polarization fluctuation component 3x arrives at the opposite station device 30.

[0087] As described with reference to Figs. 10 and 11, the opposite station device 30 constantly monitors the state of polarization in the optical transmission line 2. The opposite station device 30 also transmits frames to the optical transmission line monitoring device 40 at a predetermined period. At this time, the opposite station SOP data shown in Fig. 11 is inserted into the overhead of each frame. Here, the opposite station SOP data generated when the polarization fluctuation component 3x arrives at the opposite station device 30 is inserted into the frame 4 shown in Fig. 16. This frame 4 propagates from the opposite station device 30 toward the optical transmission line monitoring device 40. Then, the optical transmission line monitoring device 40 receives the frame 4 at time T3. It is assumed that the processing time for the opposite station device 30 to generate and transmit a frame is sufficiently short.

[0088] Here, the period from the time (T0) when the polarization fluctuation occurs in the optical transmission line 2 to the time (T3) when the optical transmission line monitoring device 40 receives the frame 4 is not longer than the RTT between the optical transmission line monitoring device 40 and the opposite station device 30. Therefore, the period from the time (T1) when the optical transmission line monitoring device 40 detects the polarization fluctuation to the time (T3) when the optical transmission line monitoring device 40 receives the frame 4 is shorter than the RTT between the optical transmission line monitoring device 40 and the opposite station device 30. Therefore, the opposite station SOP data when the polarization fluctuation component 3x arrives at the opposite station device 30 reaches the optical transmission line monitoring device 40 within the period from the time when the trigger signal is generated (i.e., the time when the optical transmission line monitoring device 40 detects the polarization fluctuation) until the RTT has elapsed. That is, the opposite station SOP data when the polarization fluctuation component 3x arrives at the opposite station device 30 should be included in the opposite station SOP data from the time when the trigger signal is generated until the time equivalent to the RTT has elapsed.

[0089] For this reason, the RTT between the optical transmission line monitoring device 40 and the opposite station device 30 is set as the period during which the similar section detection unit 50 searches for the opposite station SOP data. The RTT is "M" when converted into a frame period, and "16M" when converted into the period of the frame decimal counter 45a.

[0090] FIG. 17 shows an example of the processing of the similar section detection unit 50. The similar section detection unit 50 calculates the correlation between the reference data and the opposite station SOP data. Here, the reference data is composed of 2N local station SOP variation values. Therefore, the similar section detection unit 50 calculates the difference between the 2N local station SOP variation values ​​constituting the reference data and the 2N opposite station SOP variation values ​​in the opposite station SOP data. At this time, the similar section detection unit 50 calculates the difference between the reference data and the opposite station SOP data while shifting the reference data by one entry at a time with respect to the opposite station SOP data. Then, the section with the smallest difference is specified.

[0091] FIG. 18 is a flowchart showing an example of the process of the similar section detection unit 50. The similar section detection unit 50 is provided with the reference data and the opposing station SOP data shown in FIG. 17. The reference data is composed of 2N entries. In each entry of the reference data, a counter value (FC, FDC) indicating the local station SOP variation value and the detection time detected by the optical transmission line monitoring device 40 is recorded. The opposing station SOP data is composed of 16M entries. In each entry of the opposing station SOP data, a counter value (FC, FDC) indicating the opposing station SOP variation value and the detection time detected by the opposing station device 30 is recorded. In the following description, the local station SOP variation value constituting the reference data may be referred to as a "reference SOP variation value". Also, the SOP variation value constituting the opposing station SOP data may be referred to as a "opposite station SOP variation value".

[0092] In S1, the similar section detection unit 50 initializes variables i and j. The variable i identifies an entry constituting the reference data, and "i=1" indicates the first entry of the reference data. The variable j identifies an entry constituting the opposing node SOP data, and "j=1" indicates the first entry of the opposing node SOP data.

[0093] In S2, the similar section detection unit 50 compares the reference SOP waveform with the opposite station SOP waveform. The reference SOP waveform is represented by 2N reference SOP variation values. The opposite station SOP waveform is represented by 2N opposite station SOP variation values ​​extracted from the 16M opposite station SOP variation values. The 2N opposite station SOP variation values ​​are extracted based on the variable j. Then, the similar section detection unit 50 calculates a difference value d representing the similarity between the reference SOP waveform and the opposite station SOP waveform. In S3, the calculated difference value d is stored as a difference value D(j) corresponding to the variable j.

[0094] In S4, the similar section detection unit 50 increments the variable j. This shifts the section to be compared with the reference data. In S5, the similar section detection unit 50 judges whether or not there is any opposing station SOP data remaining to be compared with the reference data. Here, the reference data is composed of 2N entries, and the opposing station SOP data is composed of 16M entries. Therefore, if the variable j is smaller than "16M-2N+1", it is judged that there is any opposing station SOP data remaining to be compared with the reference data.

[0095] When there remains opposing station SOP data to be compared with the reference data, the process of the similar section detection unit 50 returns to S2. That is, the process of S2 to S4 is repeatedly executed while shifting the section to be compared with the reference data. At this time, a difference value D(j) is calculated for each section in the opposing station SOP data. Then, when the comparison of the entire opposing station SOP data with the reference data is completed, the process of the similar section detection unit 50 proceeds to S6.

[0096] In S6, the similar section detection unit 50 identifies the minimum difference value from among the difference values ​​D(j) calculated for each section. Then, the similar section detection unit 50 refers to the opposite station SOP data and identifies the counter value (FC, FDC) corresponding to the minimum difference value D. Note that the counter value identified by the procedure shown in FIG. 18 indicates the time when the polarization fluctuation occurring in the optical transmission line 2 arrives at the opposite station.

[0097] 19 is a flowchart showing an example of a process for comparing a reference SOP waveform with an opposing station SOP waveform. The process of this flowchart corresponds to S2 shown in FIG.

[0098] In S11, the similar section detection unit 50 initializes a variable k to "1". The variable k specifies the entry for which the comparison process should be executed. In S12, the similar section detection unit 50 initializes a variable d to "0". The variable d represents a calculated value of the comparison process between the reference SOP variation value and the opposing station SOP variation value.

[0099] In S13, the similar section detection unit 50 compares the reference SOP variation value and the opposing station SOP variation value for the entry specified by the variable k. For example, if "k=5", a comparison process is performed between the fifth reference SOP variation value and the fifth opposing station SOP variation value. The comparison process is realized, for example, by equation (3). That is, the absolute value of the difference between the kth reference SOP variation value and the kth opposing station SOP variation value is calculated. SOP_local(k) represents the kth reference SOP variation value in the reference data, and SOP_remote(k) represents the kth opposing station SOP variation value in the opposing station SOP data to be compared with the reference data.

number

[0100] Note that the formula (3) is an example of a comparison process, and the embodiment of the present invention is not limited to this method. For example, the absolute value of the difference between the square of the kth reference SOP variation value and the square of the kth opposite station SOP variation value may be calculated.

[0101] In S14, the similar section detection unit 50 adds the calculation result L in S13 to the variable d. Then, in S15, the similar section detection unit 50 increments the variable k. Then, in S16, the similar section detection unit 50 determines whether or not there are any SOP variation values ​​remaining to be compared. Here, the reference data is composed of 2N entries. Therefore, if the variable k is 2N or less, it is determined that there are any SOP variation values ​​remaining to be compared.

[0102] When there are remaining SOP variation values ​​to be compared, the process of the similar section detection unit 50 returns to S13. That is, the processes of S13 to S15 are repeatedly executed for the next SOP variation value. At this time, the new calculation result L is added to the current value of the variable d. That is, the calculation result L for each SOP variation value is cumulatively added. Then, when the comparison process has been executed for all SOP variation values, the process of the similar section detection unit 50 ends.

[0103] In this way, the similar section detection unit 50 searches for a section in which a waveform similar to the reference SOP waveform appears in the opposite station SOP data, thereby detecting the time when the polarization fluctuation generated in the optical transmission line 2 arrives at the opposite station.

[0104] The position identifying unit 51 identifies the polarization fluctuation position based on the time when the optical transmission line monitoring device 40 detects the polarization fluctuation and the time when the polarization fluctuation arrives at the opposite station. The time when the optical transmission line monitoring device 40 detects the polarization fluctuation is detected by the threshold value determining unit 48 shown in Fig. 11. The time when the polarization fluctuation arrives at the opposite station is detected by the similar section detecting unit 50.

[0105] Fig. 20 shows an example of a method for identifying the polarization fluctuation position. In Fig. 20, z represents the time taken for light to propagate from the optical transmission line monitoring device 40 to the opposing station device 30 via the optical transmission line 2. y represents the time taken for light to propagate from the polarization fluctuation position to the optical transmission line monitoring device 40 via the optical transmission line 2. x represents the time taken for light to propagate from the polarization fluctuation position to the opposing station device 30 via the optical transmission line 2. Therefore, x+y=z is obtained.

[0106] In this case, it is assumed that polarization fluctuation occurs at time T0. Then, the polarization fluctuation component 3x propagates toward the opposite station device 30, and the polarization fluctuation component 3y propagates toward the optical transmission line monitoring device 40. Then, at time T1, the polarization fluctuation component 3y arrives at the optical transmission line monitoring device 40. At this time, the optical transmission line monitoring device 40 detects that polarization fluctuation has occurred. That is, a trigger signal is output from the threshold value determination unit 48. Also, the polarization fluctuation component 3x arrives at the opposite station device 30 at time T2.

[0107] As described with reference to Figs. 10 and 11, the opposite station device 30 constantly monitors the state of polarization of the optical transmission line 2. The opposite station device 30 transmits frames to the optical transmission line monitoring device 40 at a predetermined period. At this time, the opposite station SOP data shown in Fig. 11 is inserted into the overhead of each frame. Here, the opposite station SOP data generated by the opposite station device 30 when the polarization fluctuation component 3x arrives at the opposite station is inserted into the frame 4 shown in Fig. 20. This frame 4 propagates from the opposite station device 30 toward the optical transmission line monitoring device 40. Then, the optical transmission line monitoring device 40 receives the frame 4 at time T3. In this embodiment, the process for the opposite station device 30 to generate and transmit a frame is performed by a hardware circuit such as an FPGA. Therefore, it is assumed that the processing time for the opposite station device 30 to generate and transmit a frame is sufficiently short.

[0108] In the above sequence, the time T1 at which the optical transmission line monitoring device 40 detects the polarization fluctuation occurring in the optical transmission line 2 is expressed by equation (4).

number

[0109] The time T2 at which the polarization fluctuation component 3x caused by the polarization fluctuation detected by the optical transmission line monitoring device 40 arrives at the opposite station is expressed by equation (5).

number

[0110] If the processing time required for the opposing station device 30 to generate and transmit a frame is ignored, the time T3 at which the optical transmission line monitoring device 40 receives the frame 4 is expressed by equation (6).

number

[0111] By eliminating "y" from equations (4) and (6) using "x+y=z", we obtain equation (7).

number

[0112] In this way, the time x that light takes to propagate from the polarization fluctuation position to the opposite station through the optical transmission line 2 is obtained by dividing the difference between time T1 and time T3 by 2. T1 is the time when the optical transmission line monitoring device 40 detects polarization fluctuation greater than the threshold level. Furthermore, T3 is the time when the polarization fluctuation component caused by the polarization fluctuation arrives at the opposite station, and is identified by the similar section detection unit 50. Therefore, the optical transmission line monitoring device 40 can calculate the distance from the opposite station to the polarization fluctuation position based on the propagation time x. That is, the polarization fluctuation position on the optical transmission line is identified.

[0113] The optical transmission line monitoring device 40 is realized by, for example, a calculation device such as a DSP (Digital Signal Processor) and a hardware circuit such as an FPGA (Field Programmable Gate Array). In this case, although not particularly limited, for example, the polarization state monitor 41, the similar section detection unit 50, and the position identification unit 51 may be realized by a DSP. The frame synchronization unit 42, the frame counter 43, the multiplier 44, the sampling circuit 45, the FIFO circuit 46, the opposite station data storage unit 47, the threshold determination unit 48, and the reference data generation unit 49 may be realized by an FPGA.

[0114] In this way, in the optical transmission line monitoring method according to the embodiment of the present invention, by comparing the waveform of the polarization fluctuation detected at the local station with the waveform of the polarization fluctuation detected at the opposite station, the optical transmission line monitoring device can detect the timing at which the polarization fluctuation component caused by the polarization fluctuation arrives at the opposite station. Therefore, even if the polarization fluctuation component arriving at the opposite station is smaller than a predetermined threshold level, the polarization fluctuation position can be identified.

[0115] Furthermore, in an optical transmission system in which frames are transmitted at a predetermined period, identifying the polarization fluctuation position based on the frame transmission period may result in low accuracy. For example, when the frame period is 10 μs, the error in the polarization fluctuation position is a maximum of 2 km. In contrast, in an embodiment of the present invention, a multiplier is used to speed up the frame pulse signal, thereby speeding up the sampling speed for the SOP fluctuation value. This increases the accuracy of the detection time of the polarization fluctuation, and increases the accuracy of the identified polarization fluctuation position. In the above embodiment, the error in the polarization fluctuation position is improved to 1 / 16.

[0116] <Variations> In the above-mentioned embodiment, the frame pulse is increased in speed by using a multiplier and a frame decimal counter as shown in Fig. 10 and Fig. 12. However, if the frame transmission period is sufficiently short, the optical transmission line monitoring device 40 (and the opposite station device 30) does not need to include a multiplier and a frame decimal counter.

[0117] In the above embodiment, the SOP variation value detected by the opposite station device 30 is inserted into the overhead of the transmission frame, but the embodiment of the present invention is not limited to this configuration. For example, the SOP variation value may be inserted into the payload of each frame.

[0118] In the above embodiment, the optical transmission line monitoring device 40 is implemented in an optical transmission device provided at a terminal node of the optical transmission line 2, but the embodiment of the present invention is not limited to this configuration. For example, a server computer connected to the optical transmission system may collect polarization state data from the optical transmission devices provided at both ends of the optical transmission line 2, and identify the polarization fluctuation position from the polarization state data.

[0119] In the above-mentioned embodiment, the counter in the optical transmission line monitoring device 40 and the counter in the opposite station device 30 operate independently of each other, but the embodiment of the present invention is not limited to this configuration. That is, the counter in the optical transmission line monitoring device 40 and the counter in the opposite station device 30 may be synchronized with each other. In this case, the opposite station device 30 does not need to immediately transmit the detected polarization state data, and the polarization fluctuation position can be identified by comparing the polarization state data detected by the optical transmission line monitoring device 40 with the polarization state data detected by the opposite station device 30.

[0120] In the above embodiment, the optical transmission line monitoring device 40 is provided at one end node of the optical transmission line 2, and the opposite station device 30 is provided at the other end node, but the embodiment of the present invention is not limited to this configuration. That is, the optical transmission line monitoring device 40 may be provided at both ends of the optical transmission line 2. In this case, the optical transmission line monitoring device 40 needs to have a function of transmitting the detected SOP polarization value to the opposite station. With this configuration, when a polarization fluctuation larger than a threshold level is detected at one of the end nodes, the polarization fluctuation position can be identified. [Explanation of symbols]

[0121] 1A, 1B Optical transmission equipment 2. Optical Transmission Line 2x, 2y optical fiber 30 Opposite station equipment 40 Optical transmission line monitoring device 31, 41 Polarization state monitor 32, 42 Frame Synchronization Unit 33, 43 Frame Counter 34, 44 multiplier 35, 45 Sampling circuit 35a, 45a Frame Decimal Counter 36, 46 FIFO circuit 37 SOP Data Generation Section 38 Transmission OH generation section 47 Opposite station data storage unit 48 Threshold judgment unit 49 Reference Data Generation Unit 50 Similar section detection unit 51 Location identification part

Claims

1. In an optical transmission system in which frames are transmitted bidirectionally between a pair of end nodes via an optical transmission line, an optical transmission line monitoring device is installed in a first end node of the pair of end nodes, comprising: a polarization state monitor that monitors a state of polarization of the optical transmission line; a first storage unit configured to store first polarization state data representing a state of polarization detected by the polarization state monitor; a second storage unit configured to store second polarization state data representing a polarization state of the optical transmission line detected by an opposite station device implemented in a second terminal node of the set of terminal nodes; a threshold determination unit that detects a first time that indicates a time when a polarization fluctuation component caused by a polarization fluctuation occurring in the optical transmission line arrives at the optical transmission line monitoring device by comparing a polarization fluctuation value that indicates a polarization fluctuation speed detected by the polarization state monitor with a predetermined threshold level; a reference data generating unit that generates reference data by extracting the first polarization state data in the vicinity of the first time from the first polarization state data; a similar section detection unit that detects a second time representing a time when a polarization fluctuation component caused by the polarization fluctuation arrives at the opposite station device by searching for a section having a polarization state similar to the polarization state represented by the reference data in the second polarization state data; a position identifying unit that identifies a polarization fluctuation position indicating a position where the polarization fluctuation occurs based on the first time and the second time; An optical transmission line monitoring device comprising:

2. The first time represents a time when the polarization fluctuation value detected by the polarization state monitor exceeds the predetermined threshold level.

2. The optical transmission line monitoring device according to claim 1.

3. The similar section detection unit searches for a section having a polarization state similar to the polarization state represented by the reference data, in the second polarization state data, for a time domain corresponding to a round trip time (RTT) between the optical transmission line monitoring device and the opposite station device from the first time.

2. The optical transmission line monitoring device according to claim 1.

4. the first polarization state data is composed of a plurality of polarization fluctuation values ​​detected by the polarization state monitor at predetermined time intervals; the second polarization state data is composed of a plurality of polarization fluctuation values ​​detected by the opposite station device at the time intervals, the reference data is composed of 2N polarization variation values ​​including N polarization variation values ​​immediately before the first time in the first polarization state data and N polarization variation values ​​immediately after the first time, The similar section detection unit Calculating a plurality of difference values ​​by calculating a sum of differences between 2N polarization fluctuation values ​​constituting the reference data and corresponding 2N polarization fluctuation values ​​in the second polarization state data while shifting a position of the reference data with respect to the second polarization state data; By identifying 2N polarization fluctuation values ​​in the second polarization state data corresponding to the minimum difference value among the plurality of difference values, the second time representing the time when the polarization fluctuation component caused by the polarization fluctuation arrived at the opposite station device is detected.

2. The optical transmission line monitoring device according to claim 1.

5. The position identification unit is calculating a propagation differential time by dividing the difference between the first time and the second time by two; It is determined that the polarization fluctuation occurs at a position where the light has propagated from the opposite station device through the optical transmission line by the propagation difference time.

2. The optical transmission line monitoring device according to claim 1.

6. 1. An optical transmission line monitoring system for monitoring an optical transmission line in an optical transmission system in which frames are transmitted bidirectionally between a first end node and a second end node at a predetermined frame period via an optical transmission line, the optical transmission line monitoring system comprising: an optical transmission line monitoring device provided in the first terminal node; an opposite station device provided in the second terminal node; The optical transmission line monitoring device comprises: a polarization state monitor that monitors a state of polarization of the optical transmission line; a first storage unit configured to store first polarization state data representing a state of polarization detected by the polarization state monitor; a second storage unit configured to store second polarization state data representing a polarization state of the optical transmission line detected by the opposite station device; a threshold determination unit that detects a first time that indicates a time when a polarization fluctuation component caused by a polarization fluctuation occurring in the optical transmission line arrives at the optical transmission line monitoring device by comparing a polarization fluctuation value that indicates a polarization fluctuation speed detected by the polarization state monitor with a predetermined threshold level; a reference data generating unit that generates reference data by extracting the first polarization state data in the vicinity of the first time from the first polarization state data; a similar section detection unit that detects a second time representing a time when a polarization fluctuation component caused by the polarization fluctuation arrives at the opposite station device by searching for a section having a polarization state similar to the polarization state represented by the reference data in the second polarization state data; a position identifying unit that identifies a polarization fluctuation position indicating a position where the polarization fluctuation occurs based on the first time and the second time, The opposite station device a second polarization state monitor that monitors a polarization state of the optical transmission line; a transmission frame generating unit that generates a transmission frame including a polarization fluctuation value detected by the second polarization state monitor in the frame period; a transmission unit that transmits the transmission frame to the optical transmission line monitoring device at the frame period.

1. An optical transmission line monitoring system comprising:

7. The transmission frame generator inserts a plurality of polarization fluctuation values ​​detected by the second polarization state monitor into each transmission frame.

7. The optical transmission line monitoring system according to claim 6.

8. 1. An optical transmission line monitoring method for monitoring an optical transmission line in an optical transmission system in which frames are transmitted bidirectionally between a pair of end nodes via the optical transmission line, the method comprising: monitoring a state of polarization of the optical transmission line at a first end node of the set of end nodes; storing first polarization state data representative of a state of polarization detected at the first end node; storing second polarization state data representative of a state of polarization of the optical transmission line detected at a second end node of the set of end nodes; detecting a first time representing a time at which a polarization fluctuation component caused by a polarization fluctuation occurring in the optical transmission line arrives at the first terminal node by comparing a polarization fluctuation value representing a polarization fluctuation speed detected at the first terminal node with a predetermined threshold level; generating reference data by extracting the first polarization state data in the vicinity of the first time from the first polarization state data; detecting a second time representing a time when a polarization fluctuation component caused by the polarization fluctuation arrives at the second terminal node by searching for a section having a polarization state similar to the polarization state represented by the reference data in the second polarization state data; A polarization fluctuation position indicating a position where the polarization fluctuation occurs is identified based on the first time and the second time.

2. An optical transmission line monitoring method comprising:

Images